Natural fungus could help control nematodes

University of Arkansas Division of Agriculture scientists are studying a naturally-occurring fungus that may give soybean producers some protection from soybean cyst nematodes like those devastating many east Arkansas fields this year.

Robert Riggs, plant pathologist for the Arkansas Agricultural Experiment Station, is studying a parasitic fungus that can check infestations of nematodes, microscopic worms that damage soybean roots.

Riggs said the onslaught of nematodes this season is likely the result of several causes that have been building up over the past few years.

“Use of resistant varieties kept nematode populations low for a while,” he said. “For that reason, many producers haven't been seeing evidence of nematode damage and began to believe they were gone. During this time, the nematode populations may have shifted to races for which we have few resistant soybean varieties.

“In recent years, however, planting preferences have moved toward weed control and higher yields,” he said.

Growing use of varieties with less resistance to nematodes has probably allowed nematode populations to increase. In addition, Riggs said, especially cold weather last winter probably slowed natural enemies — fungi and bacteria — that normally help keep nematodes in check.

“There have been losses to nematodes for years in many of these fields,” said Terry Kirkpatrick, director of the Nematode Diagnostic Lab at the Southwest Research and Extension Center near Hope, Ark. “But this is the first time in a long time that early symptoms have been so obvious and widespread.”

The fungus used in the study, called ARF 18, was found at the UA Cotton Branch Station near Marianna, Ark., and the Pine Tree Branch Station near Colt, Ark. “This one is a parasite that has controlled cyst nematodes in our lab, greenhouse and test plot studies,” Riggs said. “It has great promise to provide a biological control for nematodes. Tests elsewhere suggest it may work even better in fields treated with Roundup herbicide, so it could be a big plus to producers growing Roundup-ready soybeans.”

Riggs is looking for a means to package the fungus economically. In the meantime, soybean producers' best bet for avoiding losses to nematodes next year is crop rotation. “Producers should plant a non-host crop next year — cotton, corn or grain sorghum,” he said. “The following year to two years, they should plant varieties that are resistant to the race of nematodes that infests their fields. After that, nematode populations should be low enough to allow planting a susceptible variety that may provide higher yields for one year.”